I have a media comms system which we are using for live communication between director and camera operators. The complaint is that turning up the comms to 100% volume is still too quiet. I believe we have an impedance matching problem.
So I contacted the manufacturer to ask what the comm device was designed for (we have 200ohm mics right now with 64ohm headphone speakers). They responded saying the following.
-The aviation headset headphones are dynamic with an impedance of 300ohm. The comm system supplies a bias voltage of 10Vdc. Microphone impedance is 50 to 600ohm with an operating voltage of 8-28Vdc.
-It’s also OK to use aviation headsets which provide their own microphone bias voltage.
So I am a bit confused, and I seek to learn a bit more about these circuits. How can a range of 50 to 600ohm be right? Wouldn't I want to just match the impedance of the jack itself? With that in mind, I did the following test... I plugged a naked plug into the mic jack and I measured the voltage given the loads seen in the attached image (This was tested on two different communications devices within the system. Results were identical).
My math tells me that, given my measurements, the source impedance is 2.7kohm. And it seems that I was able to confirm the "10Vdc bias voltage" claim.
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Now, here are my techincal questions.
- Given my situation, what is my best bet to getting more signal from a microphone? Should I expect a lower impedance microphone to be louder or a higher impedance to be louder?
- We want to use a dynamic mic. Should I be using an isolation technique to keep the Vdc bias voltage from reaching the mic?
Shure educational material suggested this to me.
- Should I just skip this whole headache and get some inline mic preamps?
- And is it strange (or completely normal?) to have such an impedance from the bias voltage source? I mean, it seems that any typical microphone wouldn't see the full 10Vdc of bias voltage with so much of that voltage dropping before it gets out of the plug. Perhaps these mics only need 1-4V of bias voltage?
If anyone with experience in this could point me in the right direction, I would greatly appreciate it. TIA.